Wireless or mobile communications networks in which a mobile terminal (UE, such as a mobile handset) communicates via a radio link to a network of base stations (eNBs) or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations. The initial deployment of systems using analogue signaling has been superseded by second generation (2G) digital systems such as Global System for Mobile communications (GSM), which typically use a radio access technology known as GSM Enhanced Data rates for GSM Evolution Radio Access Network (GERAN), combined with an improved core network.
Second generation systems have themselves been replaced by or augmented by third generation (3G) digital systems such as the Universal Mobile Telecommunications System (UMTS), which uses a Universal Terrestrial Radio Access Network (UTRAN) radio access technology and a similar core network to GSM. UMTS is specified in standards produced by 3GPP. Third generation standards provide for a greater throughput of data than is provided by second generation systems. This trend is continued with the move towards fourth generation (4G) systems.
3GPP design, specify and standardize technologies for mobile (cellular) wireless communications networks. Specifically 3GPP produces a series of technical reports (TR) and technical specifications (TS) that define 3GPP technologies. The focus of 3GPP is currently the specification of standards beyond 3G, and in particular an Evolved Packet System (EPS) offering enhancements over 3G networks, including higher data rates. The set of specifications for the EPS comprises two work items: Systems Architecture Evolution (SAE, concerning the core network) and LTE concerning the air interface. The first set of EPS specifications were released as 3GPP Release 8 in December 2008. LTE uses an improved radio access technology known as Evolved UTRAN (E-UTRAN), which offers potentially greater capacity and additional features compared with previous standards. SAE provides an improved core network technology referred to as the Evolved Packet Core (EPC). Despite LTE strictly referring only to the air interface, LTE is commonly used to refer to the whole of the EPS, including by 3GPP themselves. LTE is used in this sense in the remainder of this specification, including when referring to LTE enhancements, such as LTE Advanced. LTE is an evolution of UMTS and shares certain high level components and protocols with UMTS. LTE Advanced offers still higher data rates compared to LTE and is defined by 3GPP standards releases from 3GPP Release 10 up to and including 3GPP Release 12. LTE Advanced is considered to be a 4G mobile communication system by the International Telecommunication Union (ITU).
The present disclosure is implemented within an LTE mobile network. Therefore, an overview of an LTE network is shown in FIG. 1. The LTE system comprises three high level components: at least one UE 102, the E-UTRAN 104 and the EPC 106. The EPC 106 communicates with Packet Data Networks (PDNs) and servers 108 in the outside world. FIG. 1 shows the key component parts of the EPC 106. It will be appreciated that FIG. 1 is a simplification and a typical implementation of LTE will include further components. In FIG. 1, interfaces between different parts of the LTE system are shown. The double ended arrow indicates the air interface between the UE 102 and the E-UTRAN 104. For the remaining interfaces media is represented by solid lines and signaling is represented by dashed lines.
The E-UTRAN 104 comprises a single type of component: an eNB which is responsible for handling radio communications between the UE 102 and the EPC 106 across the air interface. An eNB controls UEs 102 in one or more cell. LTE is a cellular system in which the eNBs provide coverage over one or more cells. Typically there is a plurality of eNBs within an LTE system. In general, a UE in LTE communicates with one eNB through one cell at a time.
Key components of the EPC 106 are shown in FIG. 1. It will be appreciated that in an LTE network there may be more than one of each component according to the number of UEs 102, the geographical area of the network and the volume of data to be transported across the network. Data traffic is passed between each eNB and a corresponding Serving Gateway (S-GW) 110 which routes data between the eNB and a PDN Gateway (P-GW) 112. The P-GW 112 is responsible for connecting a UE to one or more servers or PDNs 108 in the outside world. The Mobility Management Entity (MME) 114 controls the high-level operation of the UE 102 through signaling messages exchanged with the UE 102 through the E-UTRAN 104. Each UE is registered with a single MME. There is no direct signaling pathway between the MME 114 and the UE 102 (communication with the UE 102 being across the air interface via the E-UTRAN 104). Signaling messages between the MME 114 and the UE 102 comprise EPS Session Management (ESM) protocol messages controlling the flow of data from the UE to the outside world and EPS Mobility Management (EMM) protocol messages controlling the rerouting of signaling and data flows when the UE 102 moves between eNBs within the E-UTRAN. The MME 114 exchanges signaling traffic with the S-GW 110 to assist with routing data traffic. The MME 114 also communicates with a Home Subscriber Server (HSS) 116 which stores information about users registered with the network.
LTE is designed as a Packet Switched (PS) network that imposes no limitations on the type of data traffic that is carried. For the bulk of data traffic the data applications are implemented by third parties, or at least separate from the LTE delivery network (for instance, email and web browsing services). However, telephony services have historically been closely integrated to the delivery network and it is desirable to continue to closely integrate telephony services with the LTE network. Telephony services principally relate to voice calls and the Short Messaging Service (SMS). On top of telephony services, a range of Supplementary Services (SS) are commonly deployed in mobile communications networks, including, for instance, call waiting, call hold, call forwarding, call barring, conferencing and number identification.
There are strong commercial pressures for network operators to tightly integrate telephony services into LTE networks as the revenue that can be generated from telephony services is disproportionately large compared with general data services. If telephony services (and supplementary services) are treated like any other data traffic and provided by a third party (for instance by connecting the EPC to an externally provided Voice over IP (VoIP) service), then the revenue that can be generated is at best shared. Additionally, there are performance and quality implications for telephony services that are best served by close integration.
There are two main approaches for an LTE network operator to implement telephony and supplementary services: using an IP Multimedia Subsystem (IMS) and Circuit Switched Fall Back (CSFB).
An IMS is a separate 3GPP network which is coupled to the EPC and which provides real time IP multimedia services, including telephony services through VoIP. An IMS network coupled to an LTE network allows for voice calls that are carried from end to end as VoIP (for calls originating and terminating at UEs within the LTE network). An IMS network may also be directly connected to a GSM network, a UMTS network, other types of mobile communication network or a Public Switched Telephone Network (PSTN: a landline communications network) such that calls originating or terminating at UEs or phones outside of the LTE network are partially carried over Circuit Switched (CS) bearers. A full description of an IMS network will not be provided here as this will be well known to the skilled person, though an overview is provided below in connection with FIG. 2. It is noted only that the principal connection between the LTE network and the IMS network is through the P-GW. Additional signaling may be passed to and from the LTE network through a Policy and Charging Rules Function (PCRF) for requesting dedicated EPS bearers to carry voice calls, and which meet the necessary qualify of service requirements. The PCRF is connected to the P-GW. A subscriber to an LTE mobile communications network is able to make voice over LTE calls if they have UE that is compliant with GSMA PRD IR.92 and the network operator has a deployed IMS network. It may also be necessary for the subscriber to have a voice over LTE subscription with the network operator.
The use of an IMS network to support telephony and supplementary services is promoted by the Voice Over LTB (VOLTE) initiative of the GSM Association (GSMA). GSMA Permanent Reference Document (PRD) IR.92 (IMS Profile for Voice and SMS) defines a minimum mandatory set of features defined in the respective 3GPP technical specifications that must be implemented by a UE and network equipment in order to ensure interoperable IMS-based telephony and supplementary IMS-based services over LTE. However, some LTE networks have been deployed before deployment of an IMS network. To address the need to provide subscribers and users of those networks with telephony and supplementary services, 3GPP have standardized CSFB in 3GPP TS 23.272 (Circuit Switched (CS) Fall Back in Evolved Packet System (EPS)). Using CSFB, to place or receive a voice call, a UE falls back to a CS mobile communications network, such as GSM or UMTS. A full description of CSFB will not be provided here as this will be well known to the skilled person, though an overview is provided below in connection with FIG. 3. It is noted only that an MME communicates with a GSM or UMTS Mobile Switching Centre (MSC), which supports CSFB, across an interface designated SGs. Upon registering a UE with an MME (for instance, when the UE is first switched on) the UE is also registered with an MSC so as to place or receive CS voice calls via the CS network. To place or receive a CS voice call may require the UE to move from LTE to UMTS or GSM. This can add considerable delay to voice calls.
3GPP defines configuration parameters for voice calls and SMS that are controlled by the network operator. These are implemented in Open Mobile Alliance (OMA) Managed Objects (MO) as specified for instance in 3GPP TS 24.305 (Selective Disabling of 3GPP User Equipment Capabilities (SDoUE) Management Object (MO)) and 3GPP TS 24.167 (3GPP IMS Management Object (MO)) amongst others. However, in order to minimize complexity, GSMA PRD IR.92 seeks to minimize the use of configuration parameters set through MOs. Given that GSMA PRD IR.92 provides a profile of a minimum set of mandatory features, a large proportion of configuration parameters that are configurable by the network operator using MOs within the 3GPP specifications may be preconfigured, for instance set by the UE manufacturer.
For a UE that is only LTE capable (that is, the UE is unable to operate with CSFB and all telephony and supplementary services must be handled by an IMS network) there is no need for any MOs at all. However, as discussed above, UEs restricted to LTE are not able to function correctly on a large number of networks where CSFB is necessary, for instance to make voice calls.
For UEs also supporting CS access, then for voice and SMS support GSMA PRD IR.92 mandates in Annex A.2 that a UE must perform voice domain selection for originating sessions with the setting of “IMS PS Voice preferred, CS voice as secondary” as specified in 3GPP TS 23.221 (Architectural requirements) Section 7.2a. This does not need to be a configuration parameter specified by an MO and this can be preconfigured by the UE manufacturer. The IMS MO defined in 3GPP TS 24.167, and specifically the corresponding MO parameter “Voice_Domain_Preference_E_UTRAN” specified in section 5.27 is not used in GSMA PRD IR.92. This MO parameter also allows the restriction to CS voice only, CS voice preferred PS secondary, PS voice preferred CS secondary or PS voice only.
For UEs also supporting CS access, there may be instances where the operator would like to have control over whether a particular subscriber can be allowed to make voice calls over LTE, for instance if the subscriber is late making payments and the operator wishes to restrict the network functions available to the user. Additionally, if the subscriber has put their Subscriber Identity Module (SIM) allowing voice over LTE into a UE that does not comply with GSMA PRD IR.92, the network operator may wish to prevent the UE attempting to make voice over LTE calls. However, this restriction to using only CSFB is not currently possible under GSMA PRD IR.92.
For UEs also supporting CS access, GSMA PRD IR.92 does allow the use of an MO for SMS, specifically to support SMS over IP (using the IMS) and SMS over SGs (using the CS network across the interface between the MME and the MSC). GSMA PRD IR.92 allows the network operator to either preconfigure the UE to only use SMS over IP or only use SMS over SGs. Alternatively, the network operator can configure the UE to use SMS over SGs when required through the use of the IMS MO defined in 3GPP TS 24.167, and specifically the MO configuration parameter “SMS_Over_IP_Networks_Indication” specified in section 5.28. This MO configuration parameter allows a choice between SMS over SGs only or SMS over IP preferred SMS over SGs secondary.
For UEs also supporting CS access, the UE can use CSFB to perform call independent supplementary services (structured supplementary services) and Unstructured Supplementary Services Data (USSD) operations (operator defined supplementary services). GSMA PRD IR.92, section 2.3.2 and Annex A.4, mandates the use of the eXtendable Markup Language (XML) Configuration Access Protocol (XCAP)/Ut interface (the interface between the UE and an Application Server (AS) within the IMS) for supplementary services management setting control originating from the mobile terminal.
Supplementary services management setting control describes the ability for the user (using the UE) to interrogate (that is, view) supplementary service settings, modify existing supplementary service settings and perform deactivation/activation/deregistration/registration of existing supplementary services. An example of interrogation is when the user wishes to know what their current communication diversion number and service status is set to for a specific communication diversion supplementary service (for instance, communication diversion on busy subscriber). An example of modification of an existing setting may be to change the communication barring password that the operator normally assigns by default and the user is allowed to change. Such a password is used as authorization to change barring settings. An example of deactivation of a supplementary service is allowing the communication forwarding number to still be registered, but to just deactivate the service. An example of deregistration of a supplementary service is allowing the communication forwarding service registration data (for instance, communication forwarding number) to be removed thus also deactivating the service.
In some circumstances it is desirable to allow the use of the IMS network for supplementary services management setting control originating from the mobile terminal even where voice calls are transmitted using CSFB. For example when the UE falls back to the CS domain, nothing prevents the operator from using network based IMS Centralized Services (ICS) through a deployed MSC server enhanced for ICS. When the IMS UE connects to an MSC server enhanced for ICS, the CS voice signaling is interworked through to IMS, and the UE can still make use of XCAP/Ut to modify these service that are centralized in IMS. 3GPP (and therefore also GSMA PRD IR.92) does not specify any mechanism for the use of CSFB for supplementary services management setting control originating from the mobile terminal. A VOLTE capable UE that would normally use the XCAP/Ut interface to make supplementary services management setting control changes will continue to try to use this interface even in the event that the UE is connected to an LTE network without an IMS. Currently, the only way to prevent this is through configuration within the UE by UE manufacturers and network operators in order to try to the CSFB if the UE fails to use XCAP/Ut. However, there is no guidance for UE manufacturers how this can be done, which risks interoperability problems.